1. Field of the Invention
The present invention relates to an apparatus for performing crystal growth of a metal or a semiconductor and, more particularly, to an apparatus for performing crystal growth using a vapor-phase growth method, in which an apparatus for supplying a material gas is improved.
2. Description of the Prior Art
FIG. 8 is a sectional view of a bubbling apparatus a conventional material supplying apparatus. In FIG. 8, a container body 1 is made of SUS, a material solution 2 is stored in the container body 1, a carrier gas inlet pipe 3 has one end put into the material solution in the container body 1, and a gas outlet pipe 4 has one end disposed so as not to come into contact with the material solution 2 in the container body 1. In addition, a back pressure control valve 20 is disposed in the gas outlet pipe 4, whereby an amount of material gas to be taken out can be controlled and kept constant. In addition, a constant temperature bath 21 surrounds the container body 1 and heats it so the vapor in the container body is in a saturated state in the constant temperature bath 21.
Then, an operation of the apparatus in the crystal growth process will be described.
As shown in FIG. 8, a carrier gas (for example, hydrogen) which does not react with the material solution 2 is introduced from the carrier gas inlet introducing pipe 3 into the container body 1 storing the material solution 2, such as TMA (trimethylaluminum), TMG (trimethylgallium) or TEG (triethylgallium), and a material gas according to vapor pressure of the material and an amount of the introduced carrier gas flows out of the container with the carrier gas. Thus obtained material gas is introduced to a reaction chamber (not shown) and used for crystal growth.
According to the thus structured conventional material supplying apparatus, there is no means for displaying a residual amount of the material solution in the container or a time to exchange the material solution. Therefore, in order to prevent the material solution in the container body 1 from being exhausted, it is necessary to calculate the amount of the material used from the amount of the material consumed per unit time using the vapor pressure which depends upon temperature, the flow rate of carrier gas, and the pressure in the container, and then to estimate the time for replenishing the material solution 2 from the difference between the consumed amount of the material solution and an initial amount of the material solution.
Then, in order to solve the above-described problem, for example, Japanese Published Patent Application No. Hei. 4-363131 discloses a system in which a float is disposed in the container storing the material solution as a liquid surface sensor and the position of the liquid surface is detected by detecting a position of the float. According to the technique disclosed in this publication, the flow of the carrier gas is controlled according to the thus detected liquid surface position, whereby a decrease in concentration of the material gas supplied per unit time is compensated by increasing the amount of supply of the carrier gas. In this system, however, it is necessary to provide a moving part in the container and a sensor for detecting the position of the moving part (a float in this case), so that the structure becomes complicated and a problem in reliability or costs could be generated.
As described above, since the conventional material supplying apparatus is thus structured, the structure for detecting the position of the liquid surface in the container storing the material solution is complicated and the reliability is low.